Method of and apparatus for recovering nitrogen from air by use of a cold boiling liquid such as nitrogen



March 1, 1960 w. L. MORRISON 2,926,50

METHOD OF AND APPARATUS FOR RECOVERING NITROGEN FROM AIR BY USE OF A COLD BOILING LIQUID SUCH As NITROGEN Filed Dec. 24, 1956 m m H mm n V0 ME CM L D &0 R RT A ET L KA M w P V- B United States Patent METHOD OF AND APPARATUS FOR RECOVERING NITROGEN FROM AIR BY USE OF A COLD BOILING LIQUID SUCH AS NITROGEN Application December 24, 1956, Serial No.630,374

6 Claims. (Cl. 62-40) My invention relates to method of and apparatus for recovering nitrogen from air by the use of a cold boiling liquidsuch as nitrogen. By cold boiling liquid I mean a liquid the boiling point of which at atmospheric pressure is far below zero degrees F.

In connection with the use of liquid nitrogen as a'refrigerant brought directly into contact with the foodstuffs or other perishable materiahor their direct containers, especially when a multiplicity of interchangeable containers must be presented to the nitrogen supply, chilled and then removed, there is a continuous depletion of the nitrogen in the system even though care is taken to insure that a maximum percentage of the gaseous nitrogen boiled off from the liquid by contact with the stuff being cooled be returned for reliquefaction and reuse.

It is therefore necessary to provide-means for supplying make up nitrogen. Make up nitrogen in liquid form is an article of commerce and can be purchased but the expense is high and such refrigeration devices may work in places where liquid nitrogen make up is hard to come by. It has been suggested that such refrigerating plants be accompanied by a separate liquid air, liquid oxygen, liquid nitrogen recovery plant. This again is expensive and complicated.

This invention discloses a method and apparatus whereby with the simple addition of certain heat exchangers and a separating device and an air compressor with conventional after-cooler, the liquid nitrogen used as a refrigerant or rather some of that liquid nitrogen may be used to produce the necessary low temperatures to obtain make up nitrogen.

Other objects will appear from time to time in the A course of the specification and claims.

- My invention is illustrated in the accompanying flow sheet wherein like parts are indicated by like characters throughout the specification and drawing;

A nitrogen liquefaction plant 1 is adapted to liquefy gaseous nitrogen supplied to it and discharge the liquid nitrogen to storage at 2,-preferably though not necessarily at atmospheric pressure. A liquid nitrogen supply duct 3 controlled by the valve 4, leads to a chilling zone 5, which preferably takes the form of an insulated container adapted to hold the material to be chilled and adapted to be easily connected to and separated from the nitrogen system. The liquid nitrogen enteringthe chamber 5 isgasefied, the contents of the chamber furnishing the latent heat to change the nitrogen from liquid 2. freezer container before it reaches the reliquefier, make up nitrogen must be provided.

Liquid nitrogen at 32 0 F. may also be conducted through the pipe 9 controlled by the valve 19 to a heat exchanger 11 where aswill hereafter appear by heat exchange the liquid nitrogen is vaporized and returned at .320 F. through the duct 12 to the reliquefier.

Atmospheric air is drawn in and compressed by an air compressor 13 which for example may be two-stage, with a small horsepower percentage of that required by 1. The air will be compressed to a pressure of one hundred pounds p.s.i.g. and discharged through the duct 14 to a water after-cooler 15a which will extract most of the heat of compression. Air may then travel through the duct 16a to air cleaning or desiccating equipment 15b at for example 125 F., then through duct 16b to a first stage heat exchanger 17 Where by heat exchange this compressed air will be cooled to -227 F. by oxygen and will then as will hereafter appear be led through duct 18 to the heat exchanger 11 where by heat exchange with the liquid nitrogen, it will be cooled to -249 Ffand will be discharged through the duct 19 to the separator vessel or tall column 20. The pressure in the separator vessel is 100 pounds p.s.i.g. The temperature, 249 F. at 100 pounds p.s.i.g. is such that oxygen will liquefy but nitrogen will not, so in the vessel we have at the bottom oxygen enriched liquid and at the top gaseous nitrogen in a substantially pure state because nitrogen will not remain a liquid at -249 F. and pounds p.s.i.g. 'In order to getsatisfactory effective separation, the duct 19 extends down to a point well below the top of the separator vessel and gaseous nitrogen will be discharged therefrom through the duct 21 controlled by the pressure reduction valve 22 and led through ducts 12 and 6 to the reliquefier.

Oxygen enriched liquid from the bottom of the vessel 20 will be discharged through the duct 23, Joule T hompson expansion valve 24 and duct 25 to the heat exchanger 17. The liquid oxygen expanding from 100 pounds p.s.i.g. through the Joule Thompson valve will be in part liquid and in part gas at a temperature of approximately 297 F. and it is this cold oxygenboth in liquid and gaseous form which by heat exchange lowers the temperature .of the compressed air in the first heat exchanger. Oxygen from heat exchanger 17 will be vented to atmosphere through the duct 26 at 70 F. and atmospheric pressure, no effort being made to recover thev oxygen because in this instance, we are interested only in getting make up nitrogen gas for the refrigeration system. The fact that the make up nitrogen is supplied to the system as a gas rather than a liquid is no disadvantage because the reliquefier will always have adequate capacity to take care of and liquefy gaseous make up nitrogen just as well as gaseous nitrogen from the refrigeration chamber.

The reliquefier will, of course, include some type of compressor, presumably a multi-stage compressor. The air compressor above referred to might be built in as a part of that compressor or it might be a separate one. By control of the valves 4,7, 10 and 22, liquid nitrogen may be proportioned between refrigeration and make up or make up may be provided when refrigeration is not going on or vice versa as of course there will always be in the storage zone a substantial amount of liquid nitrogen. The temperatures and pressures above referred to are, of course, illustrative. The entire cycle might take place at atmospheric pressure but taking place at 100 pounds p.s.i.g. gives a wider range of temperature to work with, thereby improving accuracy, efiiciency and making safe and effective controls possible. The aftercooler taking out the heat of compression may, of course,

be water or air cooled or be cooled by any other means as desired.

While in a simple solution of the problem as above indicated no effort would be made to recover. the oxygen, it would, of course, under some circumstances be desirable to recover the gaseous oxygen for other usev and my invention is not limited toany particulartemperatures or pressures or methodsv of heat exchange provided only that by the use of the cold liquid nitrogen the air is reduced to a temperature at which some nitrogen may be separated from the oxygen and returned to the refrigeration system as make up.

I claim:

1. In combination, a refrigeration circuit adapted to use nitrogen as a refrigerant and a separation circuit adapted to recover nitrogen in gaseous phase from atmospheric air and supply it to the refrigeration circuit, the refrigeration circuit including in series nitrogen liquefaction means, liquid nitrogen. storage means and. a refrigeration vessel, wherein liquid nitrogen at approximately atmospheric pressure contacts material to be re.- frigerated, is evaporated thereby and from which nitrogen in gaseous phase is returned without substantial lossof temperature to the liquefaction means, the separation circuit including connected means'for compressing air, heat exchange means for cooling the compressed air by liquid coolants to a temperature between the boiling points of oxygen and nitrogen, means for supplying the resultant nitrogen in gaseous phase tot'he refrigeration circuit.

2. In combination, a refrigeration circuit adapted to use nitrogen as a refrigerant and a separation circuit adapted to recover nitrogen in gaseous phase from atmospheric air and supply it to, the refrigeration circult, the refrigeration circuit including in series nitrogen liquefaction means, liquid nitrogen storage means and a refrigeration vessel, wherein liquid nitrogen at approximately atmospheric pressure contacts materialto be refrigerated, is evaporated thereby and from which nitrogen in gaseous'phase is returned without; substantial loss of temperature to the liquefaction means, the separation circuit including connected' means. for. compressing air, heat exchangemeansfor cooling the compressed air by liquid coolants to a-temperature between the boiling points of oxygen and nitrogen, means for supplying the resultant nitrogen in, gaseous phase to the refrrger-w ation circuit, meanszfor supplying. as a coolant the liquid from which gaseous nitrogen has been extracted to the heat exchange means.

3. In combination, a refrigeration circuit adapted" to use nitrogen as a refrigerant: and a separation circuit adapted to recover nitrogen in gaseous phase from atmospheric air and supply it to the refrigeration-circuit, the refrigeration circuit including-in series nitrogen liquefaction means, liquidnitrogen storagemeans and a refrigeration vessel, wherein liquid nitrogen at approximately atmospheric pressure contacts material to be-refrigerated, is evaporated thereby and from which nitrogen in gaseous phase is returned without-substantial loss' of' temperatureto the liquefaction means, the separation circuit including connected means for compressingair, heat exchange means for cooling the-compressed'ai'r by liquid coolants toatemperature between the boiling points of oxygen and nitrogen, means for supplying the resultant nitrogen in gaseous phasetothe refrigeration circuit, means for supplying as a coolant the liquid from" which gaseous nitrogen has been extracted to the heat exchangemeans, means for supplying as a coolant liq: uidnitrogen from the, refrigeration circuit to the heat: exchangemeans, means for returning nitrogen ingaseone phase from the heat; exchange means tothe refrig; eration circuit.

adapted to recover nitrogen in gaseous phase from ataezeaoi m spheric. air. and. supply it. to the, efrig tion. circuit. the refrigeration circuit including in series nitrogen liquefaction means, liquid nitrogen storage means and a refrigeration vessel, wherein liquid nitrogen at approximately atmospheric pressure contacts material to be refrigerated, is evaporated thereby and from which nitrogen, in gaseous phase is returned without substantial loss oftemperaturev to the liquefaction means, the separation circuit including connected means for compressing air, heat exchange means for cooling the compressed air by liquid. coolants to a. temperature between the boiling points of oxygen and nitrogen, means for supplying the resultant nitrogen in gaseous phase to the refrigeration circuit, means for supplying as a coolant the liquid from which gaseous nitrogen has been extracted to the heat exchange means, means for supplying as a coolant liquid nitrogen from the refrigeration circuit to the heat exchange means, means for returning nitrogen in gaseone phase from the heat exchange means to the refrige'. eration circuit, the heat exchange means preventingany: mixingof. the compressed air with the coolant liquids; therein.

5. In combinatioma refrigeration circuit adapted to use nitrogen as a refrigerant and a separation circuit adapted to recover nitrogen in gaseous phase from atmospheric air and supply it to the refrigeration circuit, the, refrigeration circuit including inseries nitrogenlique' faction means, liquidnitrogen storage means and a refrigeration vessel, wherein liquid nitrogen at approximately atmospheric pressure contacts material to be refrigerated, is evaporated thereby and from which nitro gen in gaseous phase is returned without substantial lossof'temperature to the liquefaction means, the separation;

circuit including v connected means for compressing air, heatexchange meansforcooling, the compressed air by; liquid: coolants to a temperature between, the boiling points of oxygen and nitrogen, means for supplying theresultant nitrogen in gaseous phase to the refrigerationcircuit, means for, supplying as'a coolant liquid nitrogen from the refrigeration circuit to the heat exchange? means, means. for returning, nitrogen in gaseous phase mately atmospheric pressure contacts material to be refrigerated, isevaporated thereby and from which nitro gen in gaseous phase is returned without substantial loss of'temperature to,,the, liquefaction means, the separation circuit including connected means for compressing air, heat exchangemeans for cooling the compressed airby' liquid coolants to a temperature between the boilingpoints of oxygen and nitrogen, means for supplying the resultant nitrogen in gaseous phase to the refrigeration circuit; means for supplying as a coolant liquid nitrogen-from -the refrigeration circuit to the heat ex change means, means for returning nitrogen in gaseousphase from the heat exchangemeans'to therefrigeration' circuit, tl1=-h62ltf6XCh3fl6 means preventing any mix ng; of; the compressed'air with the coolant liquids-therema ReferencesCitedinithe file of this-patent UNITED STATES PATENTS 

1. IN COMBINATION, A REFRIGERATION CIRCUIT ADAPTED TO USE NITROGEN AS A REFRIGERANT AND A SEPARATION CIRCUIT ADAPTED TO RECOVER NITROGEN IN GASEOUS PHASE FROM ATMOSPHERIC AIR AND SUPPLY IT TO THE REFRIGERATION CIRCUIT, THE REFRIGERATION CIRCUIT INCLUDING IN SERIES NITROGEN LIQUEFACTION MEANS, LIQUID NITROGEN STORAGE MEANS AND A REFRIGERATION VESSEL, WHEREIN LIQUID NITROGEN AT APPROXIMATELY ATMOSPHERE PRESSURE CONTACTS MATERIAL TO BE REFRIGERATED, IS EVAPORATED THEREBY AND FROM WHICH NITROGEN IN GASEOUS PHASE IN RETURNED WITHOUT SUBSTANTIAL LOSS OF TEMPERATURE TO THE LIQUEFACTION MEANS, THE SEPARATION CIRCUIT INCLUDING CONNECTED MEANS FOR COMPRESSING AIR, 